Recent research on radio frequency integrated circuits (RFICs) has focused on the development of fully integrated radio receivers. There is an ongoing search for architectures that can deliver high selectivity and sensitivity, all at low cost and power consumption. It is well understood that the super-heterodyne architecture, with a high IF frequency, although difficult to integrate, has major advantages in terms of image rejection and selectivity. A major design hurdle for integrating the super-heterodyne receiver is on chip filtering. The architecture typically requires one or more high Q filters to provide good selectivity. This has been traditionally accomplished with relatively expensive off chip ceramic or Surface Acoustic Wave (SAW) filters. Extensive research has been done in the area of active on chip filtering. Much of the work is in the area of Gm-C filtering. It has been shown that at high frequencies, the use of on-chip Q-enhanced LC filters can have an advantage over the typical Gm-C filter in terms of power and dynamic range. Q-enhanced filters are easily integrated into standard technologies and are capable of operation at very high frequencies. The Q-enhanced LC filter is also easily tunable in both frequency and Q and its circuit topology is inherently simple. Research with Q-enhanced LC filters has explored several simple prototypes and higher order filters have also been investigated.
Precise tuning of high Q integrated circuit filters is essential for their correct operation. This is difficult or impossible to achieve using manual tuning methods because manual tuning methods cannot adequately accommodate environmental variations such as temperature or power supply changes. Master-Slave tuning suffers from component mismatch and disparate circuit noise in the master and slave circuits.
Another existing method of tuning continuous time filters has been proposed in U.S. Pat. No. 5,949,832 which issued Sep. 7, 1999, in which a communications signal is decoded, and a change in the bit error rate of the decoded signal compared to previous bit error rate is used to adjust the filter bandwidth. U.S. Pat. No. 5,945,889 which issued Aug. 31, 1999, and U.S. Pat. No. 6,266,522 which issued Jul. 24, 2001 provide solutions which are principally aimed at lower frequency filters using Nyquist sampling.